Method of forming tubular structures from sheet metal



April 26, 1938. J. J. BLACK 2,115,441

METHOD OF FORMING TUBULAR STRUCTURES FROM SHEET METAL Filed Feb. 1, 1957 2 Sheets-Sheet 1 '2 Sheets-Sheet 2 INVENT OR.

ATTORNEY 5 J. J. BLACK April 26, 1933. 1

METHOD OF FORMING TUBULAR STRUCTURES FROM SHEET METAL Filed Feb. 1, 1937 Patented Apr. 26, 1938 UNITED STATES LIETHOD F FORMING TUBULAR STRUC- TURES FROM SHEET METAL James J. Black, Cincinnati, Ohio, assignor to The Trailer Company of America, Cincinnati, Ohio, a corporation of Delaware Application February 1, 1937, Serial No. 123,333

2 Claims.

This invention relates to the art of forming sheet metal structures and is particularly directed to a new and improved process or method of forming sheet metal posts, or beams, or other tubular structures. These posts, or beams, or tubular structures may be used for a wide variety of purposes. As exemplary, they may form part of the framework of truck and trailer bodies.

It has been the object of the present invention to provide an improved method of forming tubular structures in a more efficient manner than has prevailed heretofore, particularly with respect to the final tube closing operation. It has been the further object to provide an improved method of fabricating tubular structures in whichmethod the number of dies required to form the structure has been reduced to a minimum.

These objects have been accomplished with the result that the tubular structures are formed more efliciently and are more uniform in shape. There has been a material lessening of die costs and the added ability to use the same dies for forming up a multitude of tubular forms. An unlimited variety of cross sectional configurations may be provided through the medium of a very simple set of dies.

Otherwise described, the present invention resides in the method of bending the sheet metal into channels of various forms and angles 'without the use of mandrels leading up to a final die operation which bends the channel or semiformed tubular structure into a completed tube in a single pass by the use of dies or pressing means approaching the semi-formed tubular structure from opposite sides and active on one side wall particularly through the open side of the channel. In other words the tubular structure is formed in sections at each side, of a bend and is thereafter completed by a. pressing action on the bend causing an articulation Orhinging action bringing the sections together.

Other objects andfurther advantages will be more fully apparent from the description of the accompanying drawings, in which:

Figure 1 is a perspective view of a length of sheet metal stock to be formed into a rectangular tube as an example of one form which may be fabricated by the method of .this invention.

Figure 2 is a perspective view showing the first step in forming the tube in which two right angle bends are produced between the angle forming dies to form a channel of the sheet metal strip.

Figure 3 is an end view of the completed channel strip. v

Figure 4 is a perspective view showing the second step in which the channel is opened by a third temporary bend along the center of its back by means of the same dies.

Figure 5 is an end view of the work, at the completion of the operation of Figure 4.

Figure 6 is a perspective view showing the third step in which the opened channel strip receives two more bends between the angle forming dies completing the forming of the four corners of the tube.

Figure 7 is an end view of the metal strip at the completion of this operation and prior to the removal of the temporary center bend. v

Figure 8 is a perspective view showing the closing of the section by removing the center bend by means of a straightening die substituted for the corner forming die for this purpose.

Figure 9 is an end view of the work after this operation.

Figure 10 is a perspective view showing the completion of the tube.

Figure 11 is an end view of the completed tube.

Figure 12 illustrates another sheet metal tubuiar structure formed by the method of this invention.

Figure 13 is a perspective view showing the completion of the tubular structure of Figure 12 by the straightening of the center bend by means of dies in the same manner as previously disclosed.

Figures 14, 15, 16 and 1'7, illustrate various other sheet metal sections which may be formed by this method, the views showing the open and closed positions of the structures as previously disclosed. 1

Referring to the. drawings, the blank strip of sheet metal stock, indicated at I0, is of the proper width to form,- after being worked, the rectangular tube form ll, shown in Figures 8 and 9. The various sections which may be fabricated by the method of this invention may be of any length required. In the drawings, for convenience, only a partial length is shown.

The initial formation of the sections is accomplished between the angle forming die I2 and stationary die IS. The dies l2 and iii are mounted in any metal breaking press suitable for this class of work. The die l2, cooperating with the die l3, has a knife-like or relatively sharp edge and the die l3, has a V-slot it; in its upper face. In performing its bending function, the upper die l2 descends upon the work which has been placed on the upper face of the die I3 across the V-slot I4. The sheet metal ii bent across the edge of the die 12, the metal being supported at each side upon the shoulders at the top of the V-slot. The degree of the angle thus formed in the work depends upon the distance the edge of the die I! descendsinto the V-slot at the upper surface of the die, which is determined by the operator of the press.

The method of this invention is put to a varied practice and is of particular value in forming sheet metal structural. beams and other forms utilized in the fabrication of the framework of truck and trailerbodies. The formation of the rectangular tube, illustrated in Figures 2 to 9,

' illustrates the method of this invention.

Referring .to Figures 2 and 3 of the drawings illustrating the first step in the method of forming the tube, the upper die is shown completing the second bend in the blank strip of metal to form it into a channel. The lines of bend are so spaced from the edges to provide bent portions i5, i5 of a width to form a side wall of the tube when'the portions are bent into the opposed relationship shown in succeeding operations.

The value of the present simplified method of forming sheet metal sections lies in the facility with which a wide variety of hollow angular sections may be formed on a standard die press utilizing but one set of bending dies for'the various forms. This method, besides permitting theshaping ofclosed tubular sections by a series of simple bending operations, also expedites the forming of any combination of angular bends to comprise a particular shape as desired.

' The flexibility of this method as to the variety of shapes which may be executed is due to the method through which the various angles are formed by direct bending between dies and elimination of the use of mandrels for defining the desired shape. Since the sections are required to be of considerable length, the use of mandrels would be difiicult and expensive.

The principle of directly forming the angles of the hollow sections between bending dies without the use of a mandrel to sustain the walls of the hollow section against collapse is predicated upon the practice hereinafter disclosed. I

After the preliminaryoperatlon of forming the blank into the channel form of Figures 2 and 3, it is obvious that it would be impossible to proceed to form the next two angles to complete the rectangle in the same manner, as the angle forming die l2 must work on the inside of the hollow tube through an open side thereof. In order to provide the required open side for the die to enter the section, the channel is now turned upside down'and bent centrally as at l6,

so as to form a shape somewhat like an M, as

ures 6 and 7. The treatment of the work at this point consists in forming'a right angle bend II medially of each of the legs of the middle portion of v the M. The resulting shape may be described as an angularly disposed pair of U- shapes Joined at the temporary break. .This operation comprises the third step in the formation of the rectangular section by this method.

Figures 8 and 9 illustrate the fourth operation in the forming of the section. This operation consists in removing the temporary bend or break previously formed and producing a straight side wall 18 which articulation or hinge action results in bringing the U-shapes to an opposed relationship, thus creating the rectangular shape of the section as shown.

As shown in Figure 8, the die I! is relatively thin, providing however a straight lower edge Ila for engaging the temporary bend. This die passes slightly below the surface of the lower die II; that is a little past the point at which it would straighten the wall I. of the tubular structure. This is done so that the wall will be straight when it springs'back a slight amount when released by the dies, which springing occurs normally after the bending of plate material.

' This brings the adjacent edges of the portions I,

I5, against the sides of the moving die and when thedie is withdrawn, these edges tend to spring together to the point where they substantially touch. There remains, however, a relatively nar-- allel wall as formed by the two portions l5, l5,

so that the adjacent edges of the two portions do not abut, there being a sufficient amount of clearance therebetween to permit the insertion and removal'of the straightening die IS.

The final step in the method of forming the hollow rectangular section is shown in Figures 10 and 11. In this operation the work is disposed between dies 2| and 22 to close the slit 20. The seam 23 thus formed at this abutment is in some instances welded shut in order to strengthen the finished beam.

Several other forms of hollow sections formed by this method are illustrated in Figures 12 to 17 of the drawings. These various cross sections are shown to illustrate the variety of configuration which may be formed by the present method. It will be readily understood from these views that the method is applicable to a large variety of shapes and sizes of beams and posts.- The forms illustrated have been fabricated by the same method as disclosed in connection with the rectangular tube with the exception of having different combinations and a greater number of right angle bends. Since the method of forming these configurations is identical to that employed in the forming of the rectangular tube, no showing is made of these steps in the drawings. The

final steps show the removal of the temporary bend for completing the semi completed forms.

Having described my invention, I claim:

1. The method of forming a tubular structure comprising the steps of bending a strip of sheet metal to form a channel,- temporarily bending the back wall of the channel by pressure applied at the back side thereof, forming additional bends in the back wall by, pressure applied through the open side of the channel for completing the side walls and, thereafter straightening the temporarily formed bend by applying pressure to it through the open side of the channel for substantially closing the tubular structure.

2. The method of forming a tubular structure from an open channel strip of sheet metal consisting of; temporarily bending the channelstrip open side ofthe channel for substantially closing 7 the same.

JAMES J. BLACK. 

